Colorization - what was it's purpose?

[Jorge_Stolfi]

What did the 15 century alchemists develop as colors for their needs:

Deep blue- basis copper carbonate pigment azurite
Bright green- basis copper carbonate piment malachit
Red brown- iron oxide pigment red ochra
Bright yellow- arsenic sulfide-pigment orpiment

But all those pigments are naturally-occurring minerals that don't need any "alchemical" processing other than grinding. 

And anyway,alchemists would have been unable to make azurite or orpiment.  Even today they require special lab equipment.

My personal opinion is that they did not have bright red color, this did not help them to paint violet or true red but brownish red.

A real red pigment used at that time would have been You are not allowed to view links. Register or Login to view. (cinnabar, a deep red mineral consisting of mercury sulfide) or You are not allowed to view links. Register or Login to view. (lead tetroxide, bright orangish red). From the Beinecke images, it is had to tell whether either were used.  I don't think we can trust the color shades we see on the creen.  The "reds" in the VMS may have been You are not allowed to view links. Register or Login to view. (ferric oxide, rusty red),

AFAIK minium was much cheaper than cinnabar, and hematite should have been cheaper. But it is not like the VMS Painter needed pigments by the pound...